[Intel-gfx] [PATCH v3] drm/i915: Disable the mmio.debug WARN after it fires

[Paulo Zanoni]

2014-12-18 10:47 GMT-02:00 Chris Wilson <chris at chris-wilson.co.uk>:
> On Thu, Dec 18, 2014 at 02:36:54PM +0200, Jani Nikula wrote:
>> On Thu, 18 Dec 2014, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>> > If we have a single unclaimed register, we will have lots. A WARN for
>> > each one makes the machine unusable and does not aid debugging. Convert
>> > the i915.mmio_debug option to a counter for how many WARNs to fire
>> > before shutting up. Even when i915.mmio_debug was disabled it would
>> > continue to shout an *ERROR* for every interrupt, without any
>> > information at all for debugging.
>> >
>> > The massive verbiage was added in
>> > commit 5978118c39c2f72fd8b39ef9c086723542384809
>> > Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
>> > Date:   Wed Jul 16 17:49:29 2014 -0300
>> >
>> >     drm/i915: reorganize the unclaimed register detection code
>> >
>> > v2: Automatically enable invalid mmio reporting for the *next* invalid
>> > access if mmio_debug is disabled by default. This should give us clearer
>> > debug information without polluting the logs too much.
>> > v3: Compile fixes, rebase.
>> >
>> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>> > Cc: Rodrigo Vivi <rodrigo.vivi at gmail.com>
>> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
>> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> > ---
>> >  drivers/gpu/drm/i915/i915_drv.h     |  2 +-
>> >  drivers/gpu/drm/i915/i915_params.c  |  6 +++---
>> >  drivers/gpu/drm/i915/intel_uncore.c | 10 ++++++++--
>> >  3 files changed, 12 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> > index 3047291ff2b9..ca9e21545063 100644
>> > --- a/drivers/gpu/drm/i915/i915_drv.h
>> > +++ b/drivers/gpu/drm/i915/i915_drv.h
>> > @@ -2430,7 +2430,7 @@ struct i915_params {
>> >     bool disable_display;
>> >     bool disable_vtd_wa;
>> >     int use_mmio_flip;
>> > -   bool mmio_debug;
>> > +   int mmio_debug;
>> >     bool verbose_state_checks;
>> >  };
>> >  extern struct i915_params i915 __read_mostly;
>> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>> > index 07252d8dc726..43c1df830531 100644
>> > --- a/drivers/gpu/drm/i915/i915_params.c
>> > +++ b/drivers/gpu/drm/i915/i915_params.c
>> > @@ -170,10 +170,10 @@ module_param_named(use_mmio_flip, i915.use_mmio_flip, int, 0600);
>> >  MODULE_PARM_DESC(use_mmio_flip,
>> >              "use MMIO flips (-1=never, 0=driver discretion [default], 1=always)");
>> >
>> > -module_param_named(mmio_debug, i915.mmio_debug, bool, 0600);
>> > +module_param_named(mmio_debug, i915.mmio_debug, int, 0600);
>> >  MODULE_PARM_DESC(mmio_debug,
>> > -   "Enable the MMIO debug code (default: false). This may negatively "
>> > -   "affect performance.");
>> > +   "Enable the MMIO debug code (default: off). "
>> > +   "This may negatively affect performance.");
>>
>> Why not describe the new behaviour here instead of a comment in
>> intel_uncore.c?
>
> Secrets and wording.
> "Enable the MMIO debug code for the first N failures (default: off). "
>
>> >  module_param_named(verbose_state_checks, i915.verbose_state_checks, bool, 0600);
>> >  MODULE_PARM_DESC(verbose_state_checks,
>> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
>> > index e9561de382aa..a3b662de1bdb 100644
>> > --- a/drivers/gpu/drm/i915/intel_uncore.c
>> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
>> > @@ -722,18 +722,24 @@ hsw_unclaimed_reg_debug(struct drm_i915_private *dev_priv, u32 reg, bool read,
>> >             WARN(1, "Unclaimed register detected %s %s register 0x%x\n",
>> >                  when, op, reg);
>> >             __raw_i915_write32(dev_priv, FPGA_DBG, FPGA_DBG_RM_NOCLAIM);
>> > +           i915.mmio_debug--; /* Only report the first N failures */
>> >     }
>> >  }
>> >
>> >  static void
>> >  hsw_unclaimed_reg_detect(struct drm_i915_private *dev_priv)
>> >  {
>> > -   if (i915.mmio_debug)
>> > +   static bool mmio_debug_once = true;
>> > +
>> > +   if (i915.mmio_debug || !mmio_debug_once)
>> >             return;
>> >
>> >     if (__raw_i915_read32(dev_priv, FPGA_DBG) & FPGA_DBG_RM_NOCLAIM) {
>> > -           DRM_ERROR("Unclaimed register detected. Please use the i915.mmio_debug=1 to debug this problem.");
>> > +           DRM_DEBUG("Unclaimed register detected, "
>> > +                     "enabling oneshot unclaimed register reporting. "
>> > +                     "Please use i915.mmio_debug=N for more information.\n");


In addition to Jani's comments: I can already see people trying to use
a literal N instead of a number and reporting to us that it's broken.

With at least the improved MODULE_PARM_DESC text that you wrote in your reply:
Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>



>> >             __raw_i915_write32(dev_priv, FPGA_DBG, FPGA_DBG_RM_NOCLAIM);
>> > +           i915.mmio_debug = mmio_debug_once--;
>>
>> /me frowns upon the bool assignment to int and bool post-decrement. It's
>> not quite IOCCC but a demonstration of things that suck about C.
>>
>> Is it on purpose that, if you've set i915.mmio_debug=N, you first
>> decrement it to zero, then enter here and set i915.mmio_debug=1 to do
>> hsw_unclaimed_reg_debug once more?
>
> Only in that, it serves as a nice post-script "oi, there are more
> errors" and that tracking been here, done that was growing the scope
> of the patch. N+2 messages is a small price to pay for having a single
> more accurate mmio warning in the dmesg rather than an unending torrent
> of "*ERROR* there is a problem, but we can't tell you what".
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
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-- 
Paulo Zanoni